The invention relates to water heating system controllers and more particularly to an electronic water heating system controller which allows a user to remotely control the operation of any water heating system, whether it is fueled by electricity, gas, oil or solar power. The controller displays the temperature of the water stored in the water heating system, providing the user with the necessary information to select an operating mode of the controller which will satisfy his particular hot water needs.
Virtually all domestic hot water heating systems in use in the United States today are customarily on at all times, controlled only by a thermostat mounted on the outer housing of the water heater. The thermostat cycles the heating system on and off to maintain the water stored within the system at a temperature near the setting of the thermostat. Although this arrangement is convenient in that it provides constantly available hot water, it results in a large waste of energy. In fact, out of the "normal" energy consumption for the typical American home, the domestic hot water heater is consistently the largest single energy user after space heating, typically accounting for 400 to 600 KWH/month, or about half of the non-space heating monthly energy bill.
In recent years, because of the energy crises which the United States has experienced, several commonly accepted conservation measures have been widely recommended to minimize the energy consumption of such water heating systems. Although fuel prices vary by type and geography, such measures have generally included adding insulation to water heater tanks, lowering the temperatures setting of the thermostat mounted on the outer housing of the water heater, adding pipe insulation to hot water pipes, and placing clock timers for cycling such systems on and off at specific times of the day (particularly where time of day electric rates are in effect) to save energy during those periods of time that the system is not normally used.
While these measures can generally result in energy savings they either do not directly address the main cause of the quantity of energy consumed by water heating systems, or if such cause is addressed, the "solution" does not compare with the level of convenience available to a user with a water heater that is customarily on at all times, nor does it maximize energy conservation.
I have found that a substantial portion of the energy consumed by an average water heating system can be due to "stand by losses", i.e., the amount of heat loss which occurs in a system that is not being used but which nonetheless maintains hot water at a preset temperature at all times for convenience sake. Because the hot water stored in the system's water storage tank is not used, it loses heat at a rate which is dependent upon the actual tank temperature versus the ambient temperature and the "R" value of the insulation surrounding the tank. The higher the difference between the two temperatures, and/or the lower the "R" value, the higher the rate of heat loss. Most of this heat loss occurs through the top of the water storage tank of the system so that over time a temperature stratification of the water stored in the tank occurs, i.e., the water at the top of the tank will be the hottest, while the water at the bottom will be the coldest. As the hot water in the tank loses heat, the system utilizes energy that is not put to any productive use except to heat the stored water to provide the convenience of having constantly available hot water.
From this, it can be concluded that if the hot water in the tank is not used for extended periods of time, but is simply maintained at the set temperature, stand-by losses will account for all of the energy consumption of the appliance.
I have also found that contrary to several often cited studies of average hot water use in the home, most homes do not use a small steady flow of hot water during the day with a usage peak once a day. Rather, patterns are erratic from home to home, with each home having a four to six-hour period or longer during which no hot water is used at all. If such non-use is coupled with the non-use which occurs overnight, it can be seen that stand-by losses account for a substantial portion of the average water heating system's total energy consumption.
Standby losses can also result in the inefficient operation of water heating systems using a solar preheat tank. On the assumption that standby losses are small percentage of domestic hot water energy consumption, most currently available domestic solar hot water systems are designed as two tank systems. Cold supply water is preheated in a separate preheat tank connected to solar collectors before it is added to the conventionally fueled hot water heater.
The problem with using such systems for energy conservation is that most are designed such that a user is incapable of determining whether the hot water being drawn has been heated in the solar preheat tank or in the water heater tank heated by conventional fuel such as gas, oil or electricity. If a given conventional system can experience losses as a large proportion of its total energy consumption when idle for extended periods of time, then it follows that the solar preheat tank of a solar two tank system can also experience a high level of standby losses during similar periods of time. And if these losses occur overnight when solar energy cannot replenish such losses, and if the peak usage for hot water from such system occurs in the early morning hours, it is possible that a prefectly operating and otherwise efficiently designed solar two tank preheat system will actually not supply an appreciable amount of useable solar energy so as to provide any appreciable energy savings.
One solution to the problem of stand-by losses has been the use of automatic clock timers to turn water heating systems on automatically during periods when the appliance is expected to be used and to turn the system off at times when it is expected that the appliance will remain idle. Appliance controls and timers have been designed to be installed as close to the water heating system as possible. This is because most hot water heaters are powered by 240 volts ac and range in power from 1,000 to 5,500 watts, if electric, and if gas, they require a fairly substantial gas conduit. Thus, these requirements place severe limitations upon the distance from the appliance that such control switching can be performed. The practice of placing such timers near the water heating system compromises the convenience provided because it is usually necessary for a user to go to a remote location such as a basement to change the settings of the timer. Thus, common practice is to set such clock timers for very limited, universally acceptable off periods, e.g., midnight to 5:00 A.M., with the balance of the 24 hour period being used to keep the water heater on for the sake of convenience. Thus, such timers are not very energy efficient because they generally require a water heating system to operate for long periods during the day when no hot water is needed merely for the sake of convenience, resulting in unnecessary energy consumption due to standby losses.